Transcriptomic Characterization Of The Oxidative Stress Response In Bifidobacterium Longum Subsp.Longum BBMN68and Functional Analysis Of Differentially Expressed Genes

Bifidobacteria has been considered beneficial to the human health, but their application in food industry is hindered by their high sensitivity to oxygen. Thus, it is essential to reveal the mechanism of oxidative stress response and improve the oxidative stress tolerance of bifidobacteria. This study combined transcriptomics and functional genomics method to identification and functional analysis of key genes involved in Bifidobacterium longum BBMN68response to oxygen exposure. The results will provide more valuable information for comprehensively understanding the mechanism of oxidative stress response in bifidobacteria, and also provide new insights for improve the viability of bifidobacteria in food processing. The research contents and results as follows:Morphology and surface properties changes of B. longum BBMN68under oxygen stress condition. From cell morphology observation and surface properties characterization of B. longum BBMN68exposure to oxygen, the auto-aggragation and surface hydrophobicity are strengthend, as well as the intracellular polyphosphate granules are gradually formed along with the increased oxidative stress extent and time. The result indicated that B. longum may defense against oxidative stress through change the cell surface structure and meanwhile produce polyphosphate as molecular chaperone to protect protein.Globle transcriptome profile of B. longum BBMN68exposure to oxygen and bioinformatics analysis of differential expressed genes. Using RNA-seq to determine the gene transcriptional changes in B. longum BBMN68response to oxygen exposure, and evaluate the differential expressed genes’function and probable metabolic pathway involved by bioinformatics analysis. The result demonstrated that B. longum BBMN68oxygen stress response is a overall and complex process refer to whole genome, including a series of defense and adaptation mechanisms, degradation of reactive oxygen species (ROS) and keeping redox homeostasis; indction of general stress response for nucleic acids and proteins repair; the adaptative modulation of central mentabolic processes and so on.Functional characterization of differential expressed genes involved in oxidative stress response by heterologous overexpression. Further studies are performed by overexpression and functional identification of5differential expressed and interested genes related to oxidative stress response. The results suggested that AhpC is the primary scavenger of endogenous H2O2generated by aerobic metabolism. For response to oxidative stress, AhpC also interact with other antioxidative genes, promote or active the different electron acceptor, such as thioredoxin, or other ROS scavenge pathway based on NAD(P)H.The effect on antioxidative property and native antioxidative system by engineered antioxidative proteins in B. longum. Through combination of heterogeneous catalase and superoxide dismutase in B.longum NCC2705, greatly reduced intracellular peroxides, protect nucleic from free radical injury, substabtially improved cell viability under oxidative stress conditions. It’s worth noting that incorporation of KAT and SOD can effectively compensate native antioxidative system, including TrxB1and HemN which involved in scavenge reactive oxygen species, suf operon involved in Fe-S protein biosynthesis, DNA protection protein Dps, DnaK and Lpd2involved in protein repair.